Fin-tube heat exchanger collar, and method of making same

ABSTRACT

A collar for a fin-tube heat exchanger is provided. The collar extends outwardly from a thermally conductive plate in order to receive a tube. The collar generally includes a wall having a proximal end integral to the conductive plate, and a distal end defining an opening configured for receiving a tube. The wall includes a reflare portion at its distal end, with the reflare portion being curled into either the inner diameter or the outer diameter of the wall. Preferably, the reflare portion is curled into the inner diameter of the wall, and then further flared outwardly to form a double flare. A method for forming the double flare collar is also provided. The method involves progressively moving fin stock through a metal-stamping machine in order to sequentially form double flare collars.

STATEMENT OF RELATED APPLICATIONS

The present application claims priority to Provisional PatentApplication Ser. No. 60/666,120 filed Mar. 29, 2005. (Confirmation No.4704.) That application is entitled “Fin-Tube Heat Exchanger Collar, andMethod of Making Same.” The provisional application is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to the field of heating and airconditioning systems. More specifically, the present invention pertainsto the assembly of a fin-tube heat exchanger in a heating or airconditioning system.

2. Description of the Related Art

Heating, ventilation and air conditioning systems are commonly used tocontrol indoor air temperature. In geographical areas experiencing hotor humid conditions, the circulation of refrigerated air through airducts and into a home or office provides much needed comfort. Inaddition, the process of chilling circulated air results in the removalof a percentage of moisture suspended in the air. This, in turn, reducesthe presence of mold and mildew in the indoor environment so as toimprove occupants' health.

A conventional air conditioning system employs a refrigerant forchilling air. The refrigerant is a chemical that is easily convertedfrom a gas to a liquid, and then back to a gas again. A common exampleis Freon™, which is an example of a nonflammable chlorofluorocarbon, or“CFC.” The chemical refrigerant may more generically be referred to as a“working fluid.”

To induce the cyclical phase change of the refrigerant, the refrigerant,or “working fluid,” is pumped from a compressor, through a condenser, toan evaporator, and then back to the compressor. When the working fluidleaves the condenser it is in a cooled liquid state. The refrigerantthen moves through a series of tubes in the evaporator. The tubes act asa heat exchanger when air is moved across them and through the system.

The tubes are commonly fabricated from copper or a copper-based alloydue to its corrosion-resistant properties and favorable thermalconductivity. In some instances, the copper tubes are fabricated fromcopper deoxidized by phosphorous. The tubes define elongated tubularbodies, and may have an outer diameter of 5 mm, ¼″, 7 mm, 5/16″, ⅜″, ½″,⅝″, 1″, or some size intermediate thereto.

Connected to the evaporator/condenser is a fan. When activated, the fancauses air to blow across the coils as it circulates air inside of abuilding . Movement of air across the coils causes the air to be chilledto a point near or below the dew point. Thus, the evaporator serves as aheat exchanger for cooling air by removing heat from the air.

In order to improve the efficiency of the evaporator/condenser, aplurality of fins may be mechanically connected to the tubes. Thefin-and-tube arrangement forms what is known as a fin-tube heatexchanger. Connection of the fins to the tubes is made by first forminginsert openings in the respective fins at corresponding coordinates inthe fins. The tubes are then moved through the insert openings ofadjacent fins. Thereafter, a bearing or “expansion ball” or “expansiontip” is urged through each of the tubes in order to expand the outerdiameter of the tubing into frictional engagement with the surroundingfins.

As noted, a plurality of fins is provided in the evaporator. Commonly, afin density of four to fourteen fins per inch is employed. The finstypically define planar aluminum or aluminum alloy plates, althoughcopper fins may also be used. The fins are positioned in side-to-side,parallel relation to one another, with the insert openings being alignedto receive transverse tubes. Holes at different coordinates in the finswill receive different tubes so that a single fin may receive four to 20or even more tubes, depending on the size of the evaporator.

When chilled refrigerant moves through the tubing, the tubing is itselfchilled. This, in turn, causes the plurality of fins to likewise becooled by thermal conduction. In operation, as air moves through theevaporator, it contacts not only the tubes, but also the numerous finspositioned transverse to the tubes. Because the fins have been cooleddue to contact with the tubes, the fins substantially increase thecooled surface area across which air must pass as it flows through theevaporator. In this manner, the air is chilled in a more efficientmanner.

During the formation of insert openings in fins, it is known to formraised openings known as collars. The collars are formed by urging asheet of soft metal such as aluminum sequentially through a press havinga die plate. The metal is pressed against bushings on the die plate andmoved longitudinally. As the metal sheets are advanced, they are cut tothe dimensions needed for a particular heat exchanger. The end result isa plurality of collars in an aluminum sheet, each of which defines aninsert opening for receiving a tube. From there, the sheets of metal areplaced in side-by-side relation. In this manner, multiple thin finshaving insert openings with aligned collars are formed.

After the fins are positioned, the tubes are inserted through therespective aligned collars. In most instances, the collars also serve toprovide equidistant spacing between fins. Thereafter, and as notedabove, an expansion ball is urged along a length of each tube in orderto radially expand the tubes. Expansion of a tube causes the tube tofrictionally engage the surrounding collars.

It is desirable to outwardly “flare” the distal end of each collar. Thisaids in the insertion of the tubes through the various collars. Flaringalso serves to maintain equidistant spacing between the adjacent fins.In this respect, the diameter of the flare will be greater than thediameter of the wall of the collar, thereby preventing adjacent collarsfrom becoming stuck together. U.S. Pat. No. 6,513,587 entitled “FinCollar and Method of Manufacturing” discloses various methods forcreating the outward flare. The '587 patent is incorporated herein byreference in its entirety except to the extent it is inconsistent withthe teachings herein.

It has been observed that the manufacturing process for formingoutwardly flared collars may result in some splitting of the ductilemetal material of the fins. This splitting will most typically occuralong the distal end of the collar. The splitting of the collar willimpede the mechanical bond between the collar and the received tube. Ofeven greater concern, a split collar is less efficient in transferringcool energy from the tube to the surrounding fin during operation.

Therefore, a need exists for an improved method of forming collars inevaporator/condenser fins. A need further exists for a collar having agreater amount of metal material. Still further, a need exists for acollar arrangement that has improved strength and thermal transferefficiency towards its distal end.

SUMMARY OF THE INVENTION

A collar for a fin-tube heat exchanger is first provided. The collarextends outwardly from a thermally conductive plate which serves as afin for the fin-tube heat exchanger. The collar generally includes awall drawn from the thermally conductive plate and defining an openingdimensioned to receive a tube. The wall has a proximal end integral tothe wall and a distal end curled back into contact with the wall so asto form a first flare. Preferably, the wall is substantially circular inprofile, though it may be oval.

In one aspect, the first flare is curled inwardly into the innerdiameter of the wall. Alternatively, the first flare may be curledoutwardly into the outer diameter of the wall. Preferably, the distalend has a greater outer diameter than an outer diameter of the proximalend, thereby forming a second or “double” flare.

A fin for a fin-tube heat exchanger is also provided. The fin includes athermally conductive plate. In addition, the fin includes a plurality ofdouble flare collars within the plate forming an array. Each collarcomprises a radial wall drawn from the plate and defining an openingdimensioned to receive a tube. Each wall also has a proximal endintegral to the plate and a distal end curled back into contact with thewall so as to form a first flare. The distal end of each respective wallis flared outwardly to provide a greater outer diameter than an outerdiameter of the respective proximal ends of the walls. In this way,double flare collars are formed.

In addition, a fin-tube heat exchanger is offered. The exchangerincludes at least one elongated tube received through through-openingsin a plurality of thermally conductive parallel plates. Thethrough-openings are formed from substantially cylindrical wallsextending from each of the plates. Each wall defines a proximal endintegral to the conductive plate, and a distal end forming an openingconfigured for receiving the tube. The distal end of each wall is curledback into contact with its respective wall so as to form a first flare.In addition, each distal end may have a greater outer diameter than anouter diameter of its respective proximal ends, thereby forming aplurality of double flare collars.

In one aspect, each of the plates comprises a plurality of substantiallycylindrical walls defining double flare collars for receiving aplurality of respective tubes. Further, each of the plates hascorrelating through-openings that are aligned.

A method for forming a collar in a thermally conductive plate is alsoprovided. In one embodiment, the method includes the steps of placing athermally conductive plate within a press, and then advancing the platethrough the press in order to form a plurality of cylindricalthrough-openings in the plate. Each through-opening defines a radialwall having a distal end. The method further includes the step offurther advancing the plate through the press so as to curl the distalend around into contact with the radial wall, thereby forming collarshaving a first flare. Preferably, each of the walls has a substantiallycircular profile, although the profile may be oval or other shape.

In one aspect, the method includes further advancing the plate throughthe press so as to expand the outer diameter of each of the walls at itsdistal end, thereby forming a plurality of double flare collars. Themethod will then further include inserting a tube through at least oneof the plurality of through-openings, and expanding the tube intofrictional engagement with the respective surrounding walls.

Finally, a method for forming a plurality of collars in a thermallyconductive plate is disclosed. The method includes the steps of placinga thermally conductive plate within a press; advancing the plate throughthe press in order to form a plurality of through-openings in the plate,each through-opening defining a circular wall dimensioned to receive atube; further advancing the plate through the press so as to form afirst flare at the distal end of each of the plurality of walls wherebythe distal end of the wall is curled back into its respective wall; andfurther advancing the plate through the press so as to form an outwardflare at the distal end of each of the plurality of walls such that theouter diameter of the distal end of each wall is expanded, therebyforming a plurality of double flare collars.

In one aspect, the step of forming a plurality of cylindricalthrough-openings in the plate comprises using a pierce punch to piercethrough openings through the plate, each through-opening having aproximal end integral to the plate having a first diameter, and a distalend having a second smaller diameter. Further, the step of forming afirst flare at the distal end of each of the plurality of walls maycomprise moving a reflare punch down onto the distal end of each of thewalls, the reflare punch having a tip with a diameter that is largerthan the second diameter of each of the walls, thereby forming an inwardflare. Finally, the step of forming an outward flare at the distal endof each of the plurality of walls may comprise further moving thereflare punch downward onto the distal end of the walls so as to enlargethe second diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be better understood, certain drawings or flow charts areappended hereto. It is to be noted, however, that the appended drawingsillustrate only selected embodiments of the inventions and are thereforenot to be considered limiting of scope, for the inventions may admit toother equally effective embodiments and applications.

FIG. 1 presents a cross-sectional view of a single collar for a fin-tubeheat exchanger. This is a single “reflare” design in use today.

FIG. 1A shows a progression of steps for forming the single “reflare”collar of FIG. 1. The steps are shown through a side view of a plate.

FIG. 2 presents a cross-sectional view of a single collar for a fin-tubeheat exchanger of the present invention, in one embodiment. This isreferred to herein as a “double flare” design.

FIG. 2A shows a progression of steps for forming the “double flare”collar of FIG. 2, in one embodiment.

FIG. 2B is an enlarged view of the seventh stage from FIG. 2A. Here, aside wall and the double flare feature are more clearly seen.

FIGS. 3A-3C each show an enlarged cross-sectional view of selected stepsfrom FIG. 1A. Tooling used for these prior art steps is also shown incross-section.

FIG. 3A demonstrates a pierce step.

FIG. 3B shows an extrusion step.

FIG. 3C shows an outward “reflaring” step.

FIGS. 4A-4C each show an enlarged cross-sectional view of selected stepsfrom FIG. 2A. Tooling used for the steps is also shown in cross-section.

FIG. 4A demonstrates a pierce step. This is the same step as FIG. 3A.

FIG. 4B shows a first flaring step. In this instance, the flaring isinward.

FIG. 4C shows a subsequent outward flaring step. A “double flare” collaris thus forward.

FIG. 5 is an enlarged, cross-sectional view of a processing step forforming the double flare collar of the present invention. This viewshows a reflare punch being brought down upon a pierced collar toaccomplish the steps of FIGS. 4B and 4C.

FIG. 6 presents a portion of a fin having a plurality of completeddouble flare collars.

FIG. 7A presents a cross-sectional view of the collar of FIG. 2. In thisview, a tube has been moved through the insert opening of the collar.

FIG. 7B presents a cross-sectional view of the collar of FIG. 7A. Here,the tube is being radially expanded along a portion of its length,including a portion adjacent the collar.

FIG. 8 is a cross-sectional view of a double flare collar of the presentinvention, in an alternate embodiment. Here, both flare steps provide anoutward flare.

FIG. 9 is a perspective view of a portion of a fin-tube heat exchangerhaving a plurality of fins. Double flare collars receive tubes of theexchanger.

DETAILED DESCRIPTION Definitions

As used herein, the term “fin-tube heat exchanger” means any heatexchanger that employs tubes for receiving a working fluid, and aplurality of adjacent plates that receive the plurality of tubes andwhich conduct thermal energy from the tubes for changing the temperatureof air passed across the tubes and plates. The fin-tube heat exchangermay operate to add heat to circulated air, or to remove heat fromcirculated air.

The term “plate” refers to any substantially flat, thermally conductiveobject of any dimension. The term is intended to encompass not onlysheets of material that are literally flat, but also sheets that havecorrugated surfaces, sinusoidal profiles, serrated profiles, raisedlance or other profiles designed to enhance heating or coolingefficiency as air is circulated across the plate.

Description of Specific Embodiments

FIG. 1 presents a cross-sectional view of a single collar 115 for afin-tube heat exchanger. This is a single “reflare” design in use today.The fin stock, or “plate” is partially seen at 100. A wall of the collar115 is shown at 112. The wall 112 has been extruded from the plate 100during a metal pressing process. The wall 112 may be either circular oroval in shape. A distal end of the collar 115 is seen at 114.

It is seen from the prior art collar 115 that the distal end 114 isflared outwardly. This flaring is known in the metal tooling industry asa “reflare.” This is something of a misnomer, as the distal flaring isreally the first flaring imposed upon the wall 112 of the collar 115.(Earlier stages for forming the wall 112 are actually draw stages, notflaring steps.) Therefore, this flare feature is referred to herein as asingle “flare.”

FIG. 1A shows a progression of steps for forming the single flare collar115 of FIG. 1. The steps are schematically shown through a side view offin stock 100. The fin stock 100 is taken through a series of stages,culminating in the forming of a collar 115. It is understood that eachof these stages is performed using a metal stamping machine (not shown)having selectively formed bushings (also not shown) above and/or belowthe fin stock 100 in order to form the collars 115. It is alsounderstood that in actual practice, the fin stock 100 will be pressedinto a fin having a plurality of collars 115 as the fin is progressivelymoved through the metal stamping machine. About two to twenty stampingsteps may be provided in order to form collars 115 in plate 100.

A first stage 101 is a draw stage. Here, a hemisphere-profile or“bubble” is formed in the fin stock 100. No through-opening is yetformed.

A second stage 102 is also a draw stage. Here, the profile of thepre-formed collar is flattened at the top.

A third 103 and a fourth 104 stage are also each draw stages. In thesestages, the width of the flattened profile is progressively reduced. Inthis manner, the collar is being formed to the desired height and width.It will be understood by those of ordinary skill in the art thatintermediate stages before and between the third 103 and fourth 104stages may be employed.

A fifth representative stage 105 is a piercing stage. Side walls 112 anda through-opening 125 are now formed. It is understood that thethrough-opening 125 is radial, i.e., circular or oval, meaning that theopposing side walls 112 are actually one continuous wall. It is againnoted that the fifth stage 105 is representative of a piercing stage,and is not necessarily the numerically fifth stage in the metal stampingprocess. More than four previous stages may be applied.

In a sixth stage 106, the side walls 112 are extruded or extendedupwards away from the fin stock 100. The side wall 112 has a distal end114 away from the fin stock 100. It is noted that the fifth stage 105and the sixth stage 106 are demonstrated as separate steps. However, itis possible to combine these stages 105, 106 in a single stampingprocess.

Finally, a seventh stage 107 is a flare stage. In this stage, the distalend 114 of the wall 112 is flared outwardly to form a single flare. Theresult is that the distal end 114 has a larger diameter than the wall112. Distal end 114 of FIG. 1A corresponds to distal end 114 of FIG. 1.

It is again noted that the various stages 101, 102, 103, 104, 105, 106,107 are representative, and are not intended to be exclusive. Thus,additional metal forming stages may and most likely are utilized duringthe metal stamping process to form the most thermally efficient collar115.

The collar 115 of FIG. 1 and FIG. 1A has a disadvantage in that theflared distal end 114 may crack or split during the fabrication process.Expansion of a tube received within the through-opening 125 of thecollar 115 may cause further cracking and splitting of the collar 115.Cracking reduces the bond between the tube and the surrounding collar115, that is, the collar formed from stage 107. It also decreasesthermal conduction into the collar 115 and surrounding plate 100.Therefore, a need exists for an improved collar design that is resistantto cracking.

FIG. 2 presents a cross-sectional view of a single collar 215 for afin-tube heat exchanger of the present invention, in one embodiment.This is referred to herein as a “double flare” design. As with thecollar 115 of FIG. 1, the collar 215 of FIG. 2 is formed from and isintegral with a fin stock, or “plate.” The fin stock is partially seenat 100. A wall of the collar 215 is shown at 212. The wall 212 has beendrawn from the plate 100 during a metal pressing process. The wall 212may be either circular or oval in shape. The wall 212 has a proximal end211 integral to the plate 100, and a distal end 214 defining athrough-opening 225.

It is seen from FIG. 2 that the distal end 214 of the collar 215 isagain flared outwardly. However, it is also flared inwardly by foldingover the distal end 214 into the inner diameter of the wall 212. In thisway, a “double flare” is uniquely formed. It is anticipated that thedouble flare feature will be less susceptible to cracking as compared tocollar 115 of the prior art.

FIG. 2A shows a progression of steps for forming the “double flare”collar 215 of FIG. 2, in one embodiment. A series of stages is againshown for forming collars in the fin stock 100. The fin stock 100 istaken through the series of stages, culminating in the forming of anovel collar 215. Collar 215 correlates to collar 215 of FIG. 2. It isagain understood that each of these stages is performed using a metalstamping machine (not shown) having selectively formed bushings (alsonot shown) above and/or below the fin stock 100 in order to formcollars. It is also understood that the stages are depicted through across-sectional cut of the fin stock 100.

A first stage 201 is a draw stage. Stage 201 defines the formation of ahemisphere-profile in the fin stock 100.

A second stage 202 is likewise a draw stage. Here, the pre-formed collaris flattened at the top.

A third 203 and a fourth stage 204 each demonstrate that the width ofthe flattened profile in the pre-formed collar is progressively reduced.

A fifth stage 205 is a piercing stage. A side wall 220 and athrough-opening 225 are now formed. The through-opening 225 ispreferably circular.

A sixth stage 206 shows that the side wall 212 is “flared” downwardly.

Finally, a seventh stage 207 demonstrates that the distal end of theflared side wall 212 is flared outwardly. In this way, a “double flare”is formed at the distal end 214 of the collar 215. Distal end 214 ofFIG. 2A corresponds to distal end 214 of FIG. 2. The result is that thedouble flare 214 has a larger outer diameter than the outer diameter ofside wall 212 at its proximal end 211, but has a greater thickness thanthe single flare end 114 of the collar 115 of FIG. 1.

FIG. 2B is an enlarged view of the seventh stage 207 from FIG. 2A. Here,a side wall 212 and the double flare end 214 are more clearly seen. Itis believed that the double flare end 214 will help protect againstcracking during a subsequent expansion process (shown in FIGS. 7A and7B).

It is noted that the stages 206 and 207 may and preferably are combinedinto a single step during the collar-forming process. It is alsounderstood that the various stages 201, 202, 203, 204, 205, 206, 207 arerepresentative, and are not intended to be exclusive of all steps thatmight be employed in a collar forming process. Thus, additional metalforming stages may and most likely are utilized during the metalstamping process to form the most thermally efficient collar 215.

As noted, metal pressing processes are employed in order to form thecollars 115 and 215. In connection with this process, selected tools areagain used on opposing sides of the fin stock 100. These tools includevarious configurations of bushings, punches and dies. FIGS. 3A-3C and4A-4C are offered to show certain stages in the collar formationprocesses of FIGS. 1A and 2A, respectively.

FIGS. 3A-3C show enlarged, cross-sectional views of selected steps fromFIG. 1A. Tooling used for these prior art stages is also shown incross-section.

FIG. 3A demonstrates the pierce step 105. To effectuate the pierce, apierce punch 32 is provided. The pierce punch 32 includes a tip 31 thatcontacts the distal end 114 of the metallic material used in forming thecollar 115. The tip 31 extends through the distal end 114 of the radialwall 112. The fin stock 100 and protruding radial wall 112 are supportedfrom below by a pierce die 22. The pierce die 22 includes a bushing end21 that extends upwards into the inner diameter of the wall 112. Thebushing end 21 may receive the tip 31 of the pierce punch 32 during thepiercing step 105.

FIG. 3B shows the extrusion step 106. An extrude punch 24 is placedbelow the fin stock 100. The extrude punch 24 includes a punch tip 23that is pushed upwards into the inner diameter of the wall 112 of thefin stock 100. As the punch tip 23 contacts the distal end 114 of thestock 100, the distal end 114 is straightened so that the wall 112 nowtakes on a cylindrical profile. An extrude bushing 34 is typicallyplaced above the wall 112. The extrude bushing 34 includes a bushing end33 having an inner diameter that is received over the cylindrical wall112 to maintain radial uniformity.

It is possible to combine the pierce step 105 and the extrusion step106. To do this, the bushing end 21 of the pierce die 22 is pushedupwards through the distal end 114 of the wall 112 as the tip 31 of thepierce punch 33 moves downward through the distal end 114. At the sametime, the tip 33 of the extrude bushing 34 is moved downward over theouter diameter of the wall 112. The bushing end 21 is modified to belonger so as to effectuate the straightening of the wall 112 seen instage 106.

FIG. 3C shows the outward flaring step 107. To accomplish the flaringstep 107, a reflare punch 36 is employed. The reflare punch 36 isbrought down into the inner diameter of the wall 112. The reflare punch36 defines a body having a distal tip 35. The diameter of the tip 35 issmaller than the inner diameter of the wall 112. It also has a taperededge 37 which increases in diameter away from the tip 35. As the reflarepunch 36 is pushed into the inner diameter of the wall 112, the taperededge 37 contacts the distal end 114 of the wall 112, causing the distalend 114 to flare outwardly. The result is that the distal end 114 has anouter diameter larger than the outer diameter of the wall 112 proximatethe fin stock 100. This in turn produces a single flare collar 115.

FIGS. 4A-4C show enlarged, cross-sectional views of selected steps fromFIG. 2A. Tooling used for these stages is also shown in cross-section.

FIG. 4A demonstrates the pierce step 205. To effectuate the pierce, apierce punch 32 is provided. This may be the same punch 32 as was usedin the pierce step 105 of FIG. 3A. The pierce punch 32 again includes atip 31 that contacts the distal end 214 of the metallic material 100used in forming the collar 215. The tip 31 extends through the distalend 214 of the fin stock 100 and into the radial wall 212. The fin stock100 and protruding radial wall 212 are supported from below by a piercedie 22 with a bushing end 21 that extends upwards into the innerdiameter of the wall 212. Thus, step 205 may be the same as step 105shown in FIG. 3A.

FIG. 4B shows a flaring step 206. The flaring step 206 uses a reflarepunch such as punch 36. As noted above, the reflare punch 36 defines abody having a distal tip 35. The diameter of the tip 35 is smaller thanthe inner diameter of the wall 212. At the same time, it has a diameterthat is larger than the inner diameter of the distal end 214 of the wall212 from step 205. This permits the tip 35 of the reflare punch 36 tocatch the curved distal end 214 of the wall 212 when it is brought downinto contact with the distal end 214.

FIG. 5 presents an enlarged, cross-sectional view of a processing stepfor forming the double flare collar 215 of the present invention. Thisview shows the reflare punch 36 being brought down upon the drawn collarin accordance with step 206 of FIG. 4B. In this view, the punch 36 hasnot yet contacted the distal end 214 of the wall 212.

Various dimensions are indicated in FIG. 5. These are noted as w₁, w₂,w₃, w₄ and w₅. The dimensions w₁ and w₂ represent the inside and outsidediameters of the wall 212, respectively. In one collar 215 arrangement,w₁ is about 0.385″, while w₂ is about 0.395″. This will leave about a0.005″ wall thickness on each side. The dimension w₃ represents thediameter of the tip 35 at the lower end of the taper 37, while dimensionw₅ represents the diameter of the tip 35 near the upper end of the taper37. In one aspect, this diameter w₃ is about 0.320″ while the diameterw₅ is about 0.380″. This permits the tip 35 to enter the distal end 214and dimension w₄. Finally, dimension w₄ is about 0.312″. It is againnoted that dimension w₃ must be larger than dimension w₄ to catch theinwardly curled end 214. At the same time, dimension w₃ must be smallerthan dimension w₁. Preferably, dimension w₄ is no more than 85 percentof dimension w₁. Thus, where dimension w₁ is 0.385″, dimension w₄ willbe approximately 0.327″, and preferably is 0.312″. This prevents thedistal end 214 from immediately flaring outward rather than firstflaring inward when the tip 35 is brought down into contact with thedistal end 214.

It is noted here that the dimensions provided for w₁, w₂, w₃, w₄, and w₅are merely examples. Other wall and punch tip sizes may be used.However, dimension w₄ should be no more than about 85 percent ofdimension w₁ so as to keep the distal end 214 from immediately flaringout when the punch tip 35 contacts the single-flared distal end of stage206.

FIG. 5 more clearly shows the tapered side 37 proximal to tip 35 of thereflare punch 36. The taper 37 increases in diameter away from the tip35. Typically this taper will be very small, such as less than 5°, oreven about 1°. The taper 37 may also have a shoulder 38 having an angleof approximately 30°. As the tip 35 is pushed down into the innerdiameter of the wall 212, the tapered edge 37 contacts the inwardlycurved distal end 214 of the wall 212, causing the distal end 214 toflare outwardly. The result is that the distal end 214 has an outerdiameter larger than the outer diameter of the wall 212 proximate thefin stock 100. This produces a double flare collar 215, in oneembodiment.

Returning again to FIG. 4B, it can be seen that the tip 35 has contactedthe distal end 214 of the wall 212. Downward force causes the distal end214 to fold inwardly, forming a single flare feature.

FIG. 4C shows a second flaring step 207. This is caused by furtherurging the reflare punch 36 into the inner diameter of the wall 212.This movement forces the distal end 214 of the wall 212 to be flaredoutward, meaning that the diameter of the distal end 214 is larger thanthe diameter of the wall 212 proximate the fin 100. Because the distalend 214 is reinforced with or formed of two layers of metal material,the probability of cracking at the distal end 214 is greatly diminished.The result is that the double flare end 214 has a larger diameter thanthe proximal end 211, but has a greater thickness than the single flare114 of FIG. 1. Thus, it is believed that torque resistance of the tubewithin the collar 215 is improved. Moreover, testing has demonstratedthat cooling efficiency from the tubing 40 into the fins 100 having thedouble flare collars 215 is potentially increased.

It is understood that during the metal stamping process, an array ofcollars 215 is formed. Each of the collars 215 defines a through-opening225 that is sized to receive a tube (seen at 40 in FIGS. 7A and 7B) ingenerally transverse relation. FIG. 6 presents a portion of a fin 100having a plurality of completed double flare collars 215 in such anarray.

It is also understood that fins 100 come in many different sizes, andhave different collar arrays. Oftentimes, fins are custom made accordingto a customer's design parameters. Therefore, the present inventionsshould not be limited by any fin size or collar array. Further, it isunderstood that that the steps for forming a collar of FIG. 2A are notexhaustive. In a typical metal-stamping operation, a die plate mayutilize many progressive pressing steps before a collar 215 is fullyformed.

The double flared collar 215 is preferably circular in profile, and isconfigured to circumferentially receive a tube in a heating or coolingunit. FIGS. 7A-7B demonstrate the formation of a portion of a singlefin-tube heat exchanger 700. In FIG. 7A, the plate is again seen at 100.A collar is shown at 215 in the plate 100. The collar 215 represents acompleted collar per FIG. 2. In this respect, the collar 215 includesthe wall 212 and the double flared distal end 214 forming a throughopening for receiving a tube. In FIG. 7A, a tube 40 has been insertedthrough the collar 215. However, complete frictional engagement does notyet exist between the outer diameter of the tube 40 and the collar 215.

To provide a better frictional engagement between the outer diameter ofthe tube 40 and the collar 215, a bearing (or expansion ball) isextruded through the length of the tube 40. In FIG. 7A, an expansionball is shown at 45. The expansion ball 45 is at the end of the tube 40,and has not yet entered the tube 40. A single, free expansion ball isshown. However, it is known to use other bearing arrangements, such asan elongated rod having a protruding, ball-shaped tip. The ball-shapedtip may be screwed onto the end of the rod or brazed thereon using asilver (or other) solder.

In FIG. 7B, the expansion ball 45 is being urged through the tube 40 inthe direction of arrow 42. It can be seen that along the portion of thetube 40 where the expansion ball 45 has passed, the inner and outerdiameters of the tube 40 have been enlarged. This includes the portionof the tube 40 that intersects the collar 215. By radially expanding thetubing 40 outwardly, a frictional engagement is provided between theouter diameter of the tube 40 and the collar 215.

It is understood that in the formation of the fin-tube heat exchanger700, a large number of plates 100 or fins having identically dimensionedand aligned collars 215 would receive the tube 40. Thus, FIGS. 7A and 7Bare representative of a process that takes place simultaneously in aplurality of through-openings 215.

A method for forming collars in a thermally conductive plate is alsoprovided herein. The method includes placing a thermally conductiveplate, such as plate 100, within a press. The plate 100 is advancedthrough the press in order to form a plurality of through-openings 225in the plate 100. Each through-opening defines a radical wall having adistal end 214. The plate 100 is further advanced through the press soas to form an inward flare at the distal end 214 of each of theplurality of walls 212, thereby forming double flared collars 215.

It is preferred that each of the radial walls 212 is substantiallycylindrical. It is also preferred that the plate 100 is further advancedthrough the press so as to form an outward flare at the distal end 214of each of the plurality of walls 212. In this way, “double flare”collars are provided. As noted, FIG. 6 presents a portion of a fin 100having a plurality of completed double flare collars 215.

In one embodiment, the step of forming a plurality of cylindricalthrough-openings 225 in the plate 100 comprises using a pierce punch topierce through openings through the plate. Each through-opening 225 hasa proximal end 211 integral to the plate 100 defining a first diameterw₁, and a distal end 214 defining a second smaller diameter w₄. Thediameter w₄ is a result of a piercing step, such as step 205 of FIG. 4A.

After the piercing step 205, an inward flare is formed. In one aspect,the step of forming an inward flare at the distal end 214 of each of theplurality of walls 212 comprises moving a reflare punch 36 down onto thedistal end 214 of each of the walls 212. The reflare punch 36 has a tip35 with a diameter w₃ that is larger than the tip diameter w₄ of each ofthe walls 212. This may be in accordance with step 206 of FIG. 4B.

In one embodiment, the step of forming an outward flare at the distalend 214 of each of the plurality of walls 212 comprises further movingthe reflare punch 36 downward onto the distal end 214 of the walls 212so as to enlarge the tip diameter. This may be in accordance with step207 of FIG. 4C. In this way, a double flare collar 215 is formed.

The through openings 225 of each of the collars 215 is dimensioned toreceive an expandable metal tube 40. In a further step, such a tube 40is inserted through at least one of the plurality of through openings225. The tube 40 is then expanded into frictional engagement with thesurrounding walls 212, as shown in FIG. 7B.

FIG. 8 presents a cross-sectional view of a double flare collar 800 ofthe present invention, in an alternate embodiment. Here, both flares areoutward flares. The collar 800 is again extruded from fin stock 100. Thecollar has a side wall 812 with a proximal end 811 and a distal end 814.The distal end 814 is curled outwardly around to the outer diameter ofthe side wall 812, and is also flared outwardly to enlarge the diameterof the wall 812 at the distal end 814.

An improved fin-tube heat exchanger is also provided herein. FIG. 9presents a perspective view of a portion of a fin-tube heat exchanger900, in one embodiment. The fin-tube heat exchanger 900 includes atleast one elongated tube 40. The tube 40 is configured to carry aworking fluid such as Freon™. The heat exchanger 900 also includes aplurality of thermally conductive plates 100 arranged in spaced-apartand parallel relation. Each plate 100 receives a tube 40 throughthrough-openings formed from collars 915. The collars 915 may be inaccordance with collar 215 of FIG. 2 or collar 815 of FIG. 8. In thisway, double flare collars are used in the improved fin-tube heatexchanger 900.

It is noted that each of the plates 100 or fins in FIG. 9 comprises aplurality of substantially cylindrical walls defining double flarecollars 915 for receiving a plurality of respective tubes 40.Correlating openings in the respective plates 100 are aligned forreceiving the tubes 40. The tubes 40 form a closed system forcirculating Freon™ through the exchanger 900.

As can be seen, an improved collar for a fin-tube heat exchanger isoffered. In addition, a method for fabricating an improved collar isoffered. Finally, an improved fin-tube heat exchanger having doubleflare collars is provided. It is understood that the embodiments shownand described for these inventions are merely illustrative, and thatother embodiments may exist within the spirit and scope of the claims,which follow.

1. A collar for a fin-tube heat exchanger, the collar extendingoutwardly from a thermally conductive plate, the collar comprising: aradial wall drawn from the thermally conductive plate and defining anopening dimensioned to receive a tube; and the wall having a proximalend integral to the wall and a distal end curled back into contact withthe wall so as to form a first flare.
 2. The collar of claim 1, whereinthe radial wall is substantially circular in profile.
 3. The collar ofclaim 1, wherein the radial wall is substantially oval in profile. 4.The collar of claim 1, wherein the first flare is curled inwardly intoan inner diameter of the wall.
 5. The collar of claim 4, wherein thedistal end has a greater outer diameter than an outer diameter of theproximal end, thereby forming a double flare.
 6. The collar of claim 1,wherein the first flare is curled outwardly into an outer diameter ofthe wall.
 7. The collar of claim 6, wherein the distal end has a greaterouter diameter than the proximal end, thereby forming a double flare. 8.A collar for a fin-tube heat exchanger, the collar extending outwardlyfrom a thermally conductive plate, the collar comprising: a wall drawnfrom the thermally conductive plate and defining an opening dimensionedto receive a tube, the wall having a circular profile; the wall having aproximal end integral to the wall and a distal end curled inwardly backinto contact with an inner diameter of the wall so as to form a firstflare; and the distal end of the wall having a greater outer diameterthan an outer diameter of the proximal end, thereby forming a doubleflare collar.
 9. A fin for a fin-tube heat exchanger, comprising: athermally conductive plate; and a plurality of double flare collarswithin the plate forming an array, each collar comprising a radial walldrawn from the plate and defining an opening dimensioned to receive atube, each wall having a proximal end integral to the plate and a distalend curled back into contact with the wall so as to form a first flare,and the distal end of each respective wall being flared outwardly toprovide a greater outer diameter than an outer diameter of therespective proximal ends of the walls.
 10. A fin-tube heat exchanger,comprising: at least one elongated tube, the tube having an outerdiameter; a plurality of thermally conductive parallel plates; asubstantially cylindrical wall extending from each of the plates, eachwall defining a proximal end integral to the conductive plate, and adistal end forming an opening configured for receiving the tube; and thedistal end of each wall being curled back into contact with itsrespective wall so as to form a first flare, and having a greater outerdiameter than an outer diameter of the respective proximal ends, therebyforming a plurality of double flare collars.
 11. The fin-tube heatexchanger of claim 10, wherein each of the walls has a substantiallycircular profile.
 12. The fin-tube heat exchanger of claim 11, wherein:each of the plates comprises an array of substantially cylindrical wallsdrawn from the plates and defining double flare collars for receiving aplurality of respective tubes; and the tubes being expanded intofrictional engagement with surrounding walls of the correspondingcollars.
 13. A method for forming collars in a thermally conductiveplate, comprising the steps of: placing a thermally conductive platewithin a press; advancing the plate through the press in order to form aplurality of through-openings in the plate, each through-openingdefining a radial wall having a distal end; and further advancing theplate through the press so as to curl the distal end into contact withthe radial wall, thereby forming collars having a first flare.
 14. Themethod of claim 13, wherein each of the walls has a substantiallycircular profile.
 15. The method of claim 13, further comprising thestep of: further advancing the plate through the press so as to expandthe outer diameter of each of the walls at its distal end, therebyforming a plurality of double flare collars.
 16. The method of claim15,: wherein each of the plurality of through-openings is dimensioned toreceive an expandable tube; and further comprising the step of insertinga tube through at least one of the plurality of through-openings. 17.The method of claim 16, further comprising the step of: expanding aportion of the tube into frictional engagement with a surrounding wallin the collar.
 18. A method for forming a plurality of collars in athermally conductive plate, comprising the steps of: placing a thermallyconductive plate within a press; advancing the plate through the pressin order to form a plurality of through-openings in the plate, eachthrough-opening defining a circular wall dimensioned to receive a tube;further advancing the plate through the press so as to form a firstflare at the distal end of each of the plurality of walls whereby thedistal end of the wall is curled back into its respective wall; andfurther advancing the plate through the press so as to form an outwardflare at the distal end of each of the plurality of walls such that theouter diameter of the distal end of each wall is expanded, therebyforming a plurality of double flare collars.
 19. The method of claim 18,wherein the step of forming a plurality of cylindrical through-openingsin the plate comprises using a pierce punch to pierce through-openingsthrough the plate, each through-opening having a proximal end integralto the plate having a first diameter, and a distal end having a secondsmaller diameter.
 20. The method of claim 19, wherein the step offorming a first flare at the distal end of each of the plurality ofwalls comprises moving a reflare punch down onto the distal end of eachof the walls, the reflare punch having a tip with a diameter that islarger than the second diameter of each of the walls, thereby forming aninward flare.
 21. The method of claim 20, wherein the step of forming anoutward flare at the distal end of each of the plurality of wallscomprises further moving the reflare punch downward onto the distal endof the walls so as to enlarge the second diameter.